China is rich in agricultural and forestry biomass resources, but biomass energy utilization has mainly relied on direct combustion for a long time, which not only has a low thermal efficiency, but also releases plenty of smoke dusts and residual ashes, thereby pollutes the environment heavily. In resent years, with the development of rural economy and the improvement of people's life standard, most of farmers tend to use convenient advanced energy, so that plenty of crop straws become waste and are abandoned in the field, even are burned on spot, which not only causes a great waste of resources, but also greatly threatens the environment and public traffic safety; furthermore, it becomes one of important factors which hinders the development of rural economy and society.
By means of pyrolysis technology, biomass can be converted into semicoke, combustible gas, tar and wood vinegar under high temperature and oxygen deprived conditions. This technology is a clean and high efficiency biomass energy conversion technology, wherein the pyrolysis reactor is the key part for realising the conversion. Currently, biomass pyrolysis reactors mainly have a plenty of types, such as fixed bed, fluidized bed, rotary kiln and spiral pyrolysis reactor and etc., wherein spiral pyrolysis reactor has the advantages of simple structure, maneuverable reaction conditions and continuous and stable operation.
Patent CN 101486921 A discloses a biomass continuous pyrolysis and carbonization apparatus with flexible spiral conveyor, wherein biomass feedstock is transported in the pyrolysis tube with spiral feeder and drying, pre-carbonization, carbonization and calcination reaction are finished therein, and the carbonization process is finished, the resulting biomass charcoal is cooled and collected or further processed after being discharged from the reactor. Since the process of biomass carbonization reaction is slow and time consuming, it needs to be remained in the pyrolysis tube for enough time to fully carbonize the raw material, and the processing capacity of the spiral pyrolysis reactor is greatly limited, and the processing efficiency is hard to be improved.
Patent application CN 102226092 A discloses a low-temperature pyrolytic carbonization method of agricultural and forestry waste and a carbonization furnace apparatus thereof, wherein the processing procedures are: pretreated biomass feedstock is fed into a drying apparatus for drying process, then the dried biomass is transported into a biomass pyrolytic carbonization apparatus while N2 is charged, the biomass low-temperature pyrolytic carbonization process is gradually finished, and pyrolysis gas, biomass tar and biomass charcoal are generated. The procedure is characterized in that the biomass pyrolytic carbonization temperature is relatively low and between 200-300° C. The same as patent CN 101486921 A, the carbonization process is all finished during the spiral propelling type feeding, the processing efficiency is relatively low, and it needs to charge N2 to maintain an anaerobic reaction environment during the reaction, which increases the cost of production.
Patent CN 102634358 A discloses an efficient selectable pyrolysis system and a using method thereof, wherein the system composition comprises a furnace body, a distiller, combustible gas nozzles and a cooling apparatus, and belongs to fixed bed pyrolysis process. During the process, firstly dried biomass feedstock is fed into the distiller. In the distiller, the material needs to be subjected to a pyrolysis and drying stage, pre-carbonization stage, pyrolytic carbonization stage, and cooling and collecting charcoal stage. In the stages, the heating time of the pyrolysis and drying stage is 10-20 minutes, the heating time of the pre-carbonization stage is 30-45 minutes, the heating time of the pyrolytic carbonization stage is 1-2 hours, wherein the time for the completion of feedstock carbonization is long. Although a plenty of gas nozzles is provided, which improves the temperature homogeneity in the reaction distiller to a certain extent, in the reaction distiller, temperature gradients will appear at both horizontal and longitudinal directions, which affects the homogeneity of pyrolysis charcoal quality. Not only does it consume time in the cooling and collecting char stage, but also the energy is not effectively used.